Non-destructive testing techniques have been developed in recent years, using high frequency electromagnetic waves including frequencies of an arbitrarily selected frequency band (to be referred to as terahertz waves hereinafter) out of from the millimeter wave to the terahertz wave region (from 30 GHz down to 30 THz). Terahertz waves are known to contain absorption lines of various different substances including those of biomolecules. Applications of the frequency range include safe imaging techniques for fluoroscopic examinations that can eliminate the use of X-rays and spectrometric techniques for looking into the bonding conditions of molecules by determining the absorption spectra and the complex permittivity values inside various substances. Further, techniques for analyzing biomolecules as well as techniques for estimating concentration and mobilities of carriers are expected.
Non-destructive examination techniques and imaging techniques using pulse signals in the order of picoseconds (or terahertz waves) have been proposed (see, inter alia, Japanese Patent Application Laid-Open No. H10-090174). These techniques relate to two-dimensional imaging. Imaging techniques for detecting scattered light from the boundary of adjacent layers showing different refractive indexes and acquiring information in the depth direction by using an incoherent electromagnetic wave source have also been proposed (see, inter alia, Japanese Patent Publication No. H06-035946).